1, origin

Twenty-four solar terms, a supplementary calendar established in the pre-Qin period and completely established in the Han Dynasty, is a knowledge system formed by observing the movement of the sun in a year and understanding the changing laws of the four seasons, climate and phenology in a year.

It divides the sun's annual trajectory into 24 equal parts, and each equal part is a solar term, starting from beginning of spring and ending with severe cold. It is not only a time standard promulgated by successive governments, but also a compass to guide agricultural production. The compass for predicting cold, warm, rainy and snowy weather in daily life is the crystallization of the long-term experience and wisdom of the working people of the Han nationality.

In ancient China, the sundial was measured by earth gauge, and the longest sun shadow was defined as "sun to day" (also called long day to day, long day to day, winter to day), and the shortest sun shadow was "short day to day" (also called short day to day and summer to day). One day in spring and autumn is the same length of day and night, which is designated as "vernal equinox" and "autumnal equinox". There were only four solar terms in Shang dynasty, but it developed to eight in Zhou dynasty and was completely established in Qin and Han dynasties. In BC 104, the taichu calendar written by Deng Ping officially set 24 solar terms in the calendar, and defined the astronomical position of the 24 solar terms.

The names of the twenty-four solar terms first appeared in Tian Zi Xun of Huainan in the Western Han Dynasty, and the concepts of Yin and Yang, four seasons, eight places, twelve degrees and twenty-four solar terms were also mentioned in the Preface of Historical Records Taishi Gong. During the period of Emperor Wu of the Han Dynasty, Luo compiled solar terms into the calendar, stipulating that the month without neutral gas was the last month of leap month.

Twenty-four solar terms refer to 24 specific festivals in the China lunar calendar, which indicate the changes of seasons. They are formulated according to the position change of the earth on the ecliptic (that is, the orbit of the earth around the sun), and each one corresponds to a certain position reached by the earth every time it moves 15 on the ecliptic.

2. Significance

Twenty-four solar terms are not only the time criterion promulgated by successive governments, but also the compass to guide agricultural production and to predict cold, warm, snow and rainy days in people's daily life. Twenty-four solar terms accurately reflect seasonal changes, which are used to guide agricultural activities and affect the food, clothing, housing and transportation of thousands of households. The twenty-four solar terms scientifically reveal the laws of astronomical and meteorological changes.

Twenty-four solar terms skillfully combine astronomy, agriculture, phenology and folk customs, resulting in a large number of related seasonal cultures, which have become an important part of China traditional culture.